Sealing of joints of automobile engines, such as a joint between an oil pan and an engine block, a joint between an engine head and a head cover, and a joint of a transmission, have hitherto been effected by the use of a liquid adhesive sealing composition. Examples of known liquid adhesive sealing compositions include alkyd resins, synthetic rubber resins, phenolic resins, acrylic resins, silicone resins, and the like.
In recent years, there has been a tendency that the joint surfaces, e.g., flange surfaces, to which an adhesive sealing composition is applied are composed of plural different materials, for example, different metals. Therefore, when heat is applied to such an adherend, the stress imposed on the sealing material on the adherend increases due to a difference in coefficient of thermal expansion among the materials constituting the adherend. As a result, the seal itself is caused to peel off or break so that the seal loses its sealing properties. In order to improve properties of an adhesive sealing composition to follow the adherend surface (hereinafter referred to as following properties), various proposals have been made to impart softness and elasticity to the sealing compound.
However, such an improvement of adhesive sealing compositions is accompanied by deterioration of sealing properties, such as chemical resistance, oil resistance, heat resistance, weather resistance, and the like. On the other hand, silicone based sealing compositions exhibit excellent elasticity and following properties but are inferior in oil resistance at high temperatures. Hence, none of the conventional sealing compositions show excellent resistance to heat and oil as well as satisfactory softness and elasticity.
In some cases, the conventional sealing compositions cause oil leakage when applied to parts which are in contact with hydraulic oil and are subjected to temperature changes due to heating. When, in particular, the adherend is composed of different materials, it is more difficult to attain satisfactory following properties.
Acrylic reactive sealing compositions are excellent in oil resistance as described, for example, in U.S. Pat. No. 3,837,963. However, they are inferior in elasticity and following properties and are not applicable to adherends composed of different materials, and particularly those subjected to a large change of temperature.